1. Field of the Invention
The instant invention relates to an emergency exit door lock system, and more particularly, the instant invention relates to an emergency exit door lock system wherein the system includes electrical circuitry for delaying transition of the lock from a locked mode to an unlocked mode while an alarm is sounding to give notice that the door is being opened without authorization.
2. Technical Considerations and Prior Art
As explained in the aforecited co-pending U.S. patent applications, there is a need for a new type of emergency exit door lock in which opening of the lock is delayed. In patent applications Ser. Nos. 929,968 and 022,110, the delay is accomplished by throttling a hydraulic fluid to retard retraction of a bolt while in U.S. patent application No. 051,724, the delay is accomplished by a timer which de-energizes an electromagnet after expiration of a selected time interval initiated by attempting to open the door. These approaches evolved from another approach in which a hydraulic door closure was used to effect the delay by reversing the operation of the hydraulic closure so as to delay opening the door rather than to delay closing the door. The instant invention is directed to an improvement of the aforementioned approaches.
As indicated in the related patent applications, there is an inherent conflict between safety and security, even though these two concerns are interrelated. This conflict becomes readily apparent when one considers the problems encountered in trying to optimize the design of emergency exit doors. At least some doors in public buildings, such as schools, theaters, auditoriums, restraurants and the like must, by law, be equipped with latches or locks which can be readily opened from within the building should there be a fire or other emergency situation. These locks and latches pose a security problem since doors which can be readily opened from inside of a building allow people within the building to easily escape with stolen articles and allow anyone they wish into the buildings. In the minds of security personnel, the security problems caused by easily openable emergency exit doors in many instances far outweigh the dangers of fire. Consequently, emergency exit doors are frequently locked with chains or other devices. This is done primarily because security problems arise on a day-to-day basis, whereas fires occur infrequently, and dangers of fire are therefore ignored. However, if emergency exits are locked, the results are often catastrophic when fires do occur and this, of course, causes fire departments great concern. The instant invention is an improvement over the aforementioned other approaches and helps to merge the dichotomy resulting from concerns of safety and security.